<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      font-size: 12px;
      zoom: 50%;
      -webkit-zoom: 50%;
      -moz-zoom: 50%;
      -o-zoom: 50%;
    }
  </style>
</head>
<body>
  <div class="box">
    我是一个盒子
  </div>
</body>
</html>